CN105916656B - The manufacturing method of oriented film - Google Patents

Abstract

The present invention provides a method for producing a stretched film, the method comprising: a pre-stretching film forming step, in which a thermoplastic resin is melt-extruded from a molding die (220), and the The thermoplastic resin is cooled and solidified to form a pre-stretched film (100); a smoothing step of smoothing both sides defining the thickness of the pre-stretched film (100); and A stretching step. In the stretching step, the pre-stretched film (100) whose both sides are smoothed is heated and stretched at least in the longitudinal direction to form a stretched film.

Description

Stretch film manufacturing method

technical field

The invention relates to a method for manufacturing a stretched film.

Background technique

When manufacturing a stretched film, prepare a film as a material, and use the method of stretching the prepared film to stretch the film. As a method for stretching a film, the following synchronous biaxial stretching method, etc. are known: The film is conveyed into a heating furnace while holding both ends of the film with clips, and in the heating furnace, the film is simultaneously heated and stretched in the longitudinal direction and the width direction by the clips holding both ends of the film.

In such a simultaneous biaxial stretching method, the film is heated and stretched to a desired stretching ratio by stretching the film in a heating furnace in the length direction and the width direction, but when stretching the film, due to the 1. Since a large stress is applied to both ends, which are the portions held by the jigs, cracks may be generated at both ends and the entire film may break from this point.

On the other hand, for example, in Patent Document 1, in order to prevent the film from breaking during heating and stretching by simultaneous biaxial stretching, a technique is disclosed in which a film before heating and stretching is held by a clip. The thickness of both ends of the film is thicker than that of the central part to strengthen the film.

prior art literature

patent documents

Patent Document 1: Japanese Patent Application Laid-Open No. 11-105131

Contents of the invention

The problem to be solved by the invention

However, in the technology of this patent document 1, the film used for heating and stretching is formed by melt-extruding a thermoplastic resin through a molding die, and therefore, due to uneven extrusion of the molding die, etc., the predetermined film Even if the both ends of the film are thickened, when the film is heated and stretched in the longitudinal direction by the simultaneous biaxial stretching method, the stress will be locally concentrated on both sides of the film. The part that becomes rough, so the film is easy to break.

The present invention is proposed in view of this actual situation, and its purpose is to provide a method for manufacturing a stretched film, which can prevent the Breakage of the film and a stretched film with excellent productivity and quality can be obtained.

solutions to problems

The inventors of the present invention found that the above object can be achieved by smoothing both sides of the film before heating and stretching the film obtained by melt extrusion from a forming die, and completed the present invention.

That is, the present invention provides a method for producing a stretched film, the method for producing a stretched film is characterized in that it includes a film forming step before stretching, and in the film forming step before stretching, thermoplastic resin is formed from After the molding die is melt-extruded, the thermoplastic resin is cooled and solidified to form a film before stretching; a smoothing step of smoothing both sides that define the thickness of the film before stretching and a stretching step in which the pre-stretched film whose both sides are smoothed is heated and stretched at least in the longitudinal direction to form a stretched film.

In the production method of the present invention, it is preferable that the smoothing in the smoothing step is performed by removing regions located at both ends in the width direction of the film before stretching.

In the production method of the present invention, it is preferable to remove a range of 30 mm or less in width from the both sides of the film before stretching in the region located at both ends in the width direction.

In the production method of the present invention, it is preferable to remove regions located at both ends in the width direction of the film before stretching by cutting.

In the production method of the present invention, preferably, in the stretching step, stretching not only in the longitudinal direction of the film before stretching but also stretching in the width direction of the film before stretching is used. The synchronous biaxial stretching method is used to heat and stretch the film before stretching.

In the production method of the present invention, preferably, in the stretching step, the pre-stretching film is heated and stretched so that the thickness of the stretched film after heating and stretching is in the range of 15 μm to 50 μm Inside.

In addition, in the production method of the present invention, it is preferable that, in the film forming step before stretching, as the thermoplastic resin, a first thermoplastic resin and a second thermoplastic resin different from the first thermoplastic resin are used. The resin is formed by melting and co-extruding the first thermoplastic resin and the second thermoplastic resin from a molding die and then cooling and solidifying the first thermoplastic resin and the second thermoplastic resin, thereby forming a The central portion made of the first thermoplastic resin, and the pre-stretched film are formed on both ends of the central portion in the width direction and at both end portions made of the second thermoplastic resin.

In the production method of the present invention, it is preferable to use a thermoplastic resin as the first thermoplastic resin and the second thermoplastic resin, that is, when forming the film before stretching by melt coextrusion The elongation at break at normal temperature of the both end portions made of the second thermoplastic resin is greater than the elongation at break of the center portion made of the first thermoplastic resin at room temperature.

In the production method of the present invention, it is preferable to use an acrylic resin as the first thermoplastic resin.

In the production method of the present invention, preferably, as the second thermoplastic resin, polycarbonate (PC) is mixed with a thermoplastic resin having a glass transition temperature lower than that of the acrylic resin. made of mixed resin.

Furthermore, in the production method of the present invention, it is preferable to use a thermoplastic resin having a glass transition temperature difference of 10° C. or less as the first thermoplastic resin and the second thermoplastic resin.

The effect of the invention

According to the present invention, it is possible to provide a method for producing a stretched film which can prevent breakage during stretching and is excellent in productivity and yield.

Description of drawings

FIG. 1 is a diagram for explaining an example of a method for producing a composite thin film in a composite thin film forming step.

Fig. 2 is a diagram for explaining a method of stretching a composite film by a simultaneous biaxial stretching method in a stretching step.

Fig. 3 is a diagram for explaining another example of a method for producing a composite thin film in a composite thin film forming step.

Detailed ways

Hereinafter, embodiments of the present invention will be described based on the drawings.

The manufacturing method of the stretched film according to this embodiment includes the following steps: a composite film forming step in which the first thermoplastic resin and the second thermoplastic resin different from the first thermoplastic resin are formed by using a T-die for forming. The thermoplastic resin is melted and co-extruded to form a composite film, and then both ends of the formed composite film are cut; and a stretching process, in which the composite film is heated and stretched along the length direction and the width direction.

Composite film forming process

The composite film forming step is a step of forming a composite film 100 by melt-coextruding the first thermoplastic resin and the second thermoplastic resin from a T-die, and cutting both ends of the formed composite film 100 . Here, FIG. 1 is a diagram for explaining a composite thin film forming process. In this embodiment, as shown in FIG. 1 , as a composite film 100 , a film including a central portion 110 , both end portions 120 formed on both ends in the width direction of the central portion 110 , and a central portion 110 are obtained. It is made of a first thermoplastic resin, and both ends 120 are made of a second thermoplastic resin. In addition, the central portion 110 of the composite film 100 is a portion that is heated and stretched in a stretching step described later to become a stretched film. In addition, the both ends 120 of the composite film 100 are used to reinforce the central portion 110 when the composite film 100 is heated and stretched. After the composite film 100 is heated and stretched, the both ends 120 can be removed by cutting as necessary. When cutting the composite film 100 , it is desirable to completely remove both end portions 120 by cutting a part of both end portions of the central portion 110 . In this case, a part of both ends of the central part 110 is also removed, but it is preferable to remove all the parts held by the jig 310 described later.

In the composite film forming step, first, the first thermoplastic resin and the second thermoplastic resin are supplied to the T-die 220 through the supply block 210 in a heated and melted state.

In this embodiment, a first melt extruder (not shown) for melt extruding the first thermoplastic resin and a second melt extruder for melt extruding the second thermoplastic resin are connected to the supply head 210, respectively. machine (not shown). These melt extruders are not particularly limited, and any of a single-screw extruder and a twin-screw extruder can be used. In addition, in this embodiment, each melt extruder melt-extrudes the first thermoplastic resin at a temperature equal to or higher than the melting point (melting) temperature of the first thermoplastic resin, and the melting point (melting) temperature of the second thermoplastic resin The second thermoplastic resin is melt-extruded at the above temperature, and the first thermoplastic resin and the second thermoplastic resin are supplied to the supply head 210 .

In addition, when supplying the first thermoplastic resin and the second thermoplastic resin to the T-die 220 from the supply head 210, the supply of the first thermoplastic resin and the second thermoplastic resin is performed as follows, that is, the compound obtained by the T-die 220 As shown in FIG. 1 , the film 100 is configured such that both end portions 120 made of a second thermoplastic resin are formed at both ends of a central portion 110 made of a first thermoplastic resin.

Specifically, the feed head 210 is provided with an inlet for supplying the first thermoplastic resin and, relative to the inlet for supplying the first thermoplastic resin, an inlet for widening the T-die 220 (Japanese: The inlets for the second thermoplastic resin are supplied on both sides in the horizontal direction). In addition, in this embodiment, the first thermoplastic resin and the second thermoplastic resin respectively flowed in from the inlet of the supply block 210 are merged in the supply block 210, and the first thermoplastic resin and the second thermoplastic resin flow in the supply block 210. The outlet flows out in such a manner that the first thermoplastic resin flows toward the central portion and the second thermoplastic resin flows toward both end portions of the first thermoplastic resin with respect to the widening direction of the T-die 220. , and supplied to the T-die 220.

And, in the T-die 220, the first thermoplastic resin and the second thermoplastic resin supplied from the supply head 210 are arranged in the width direction (the first thermoplastic resin and the second thermoplastic resin) by the manifold 221 provided in the T-die 220. The direction in which the resins are arranged) is widened, whereby the first thermoplastic resin and the second thermoplastic resin are co-extruded from the die lip 222 in a sheet shape.

Next, as shown in FIG. 1 , the first thermoplastic resin and the second thermoplastic resin in the form of a co-extruded sheet are continuously drawn and pinched by the touch roll 230 and the cooling roll 240, so that the first thermoplastic resin and the second thermoplastic resin It is cooled and solidified to produce a composite film 100 including a central portion 110 made of a first thermoplastic resin and both end portions 120 formed at both ends of the central portion 110 and made of a second thermoplastic resin.

In addition, in the present embodiment, the produced composite film 100 is continuously cut by the cutter 250 at positions of a predetermined width from both side surfaces of the both ends 120, whereby the two sides of the predetermined film thickness are cut. The side surface (the surface that becomes the side surface during melt extrusion through a molding die) becomes smooth. In this way, according to this embodiment, in the stretching process described later, when the composite film 100 is heated and stretched by stretching the both ends 120 of the composite film 100, it is possible to prevent the The local stress concentration caused by the roughness can prevent cracks from occurring at both end portions 120 and can improve the productivity of the stretched film.

In addition, the smoothing of the side surfaces of the both end portions 120 may be performed to such an extent that the unevenness of the side surfaces of the both end portions 120 is reduced and stress does not concentrate on a part of the both end portions 120 when the composite film 100 is stretched in the longitudinal direction. Can.

In addition, as the cutter 250, if it can make the side surfaces of the two ends 120 well smoothed by cutting, it can be any appliance, for example, a scraper (Japanese: レザー切) can be used, and a circular upper blade and a circular upper blade can be used. Rotary cutters in which the lower blades cut while rubbing against each other while continuously rotating, and laser cutters that use solid-state lasers, semiconductor lasers, liquid lasers, or gas lasers, etc., can reduce the force applied during cutting. From the viewpoint of reducing the stress of the composite film 100 and preventing cracks in the composite film 100 during cutting, it is preferable to use a laser cutter.

Moreover, when cutting the both ends 120 of the composite film 100, it is preferable to cut while heating both ends 120. Thereby, the side surfaces of both end portions 120 can be made smoother, and it is possible to more appropriately prevent the composite film 100 from breaking when the composite film 100 is heated and stretched.

In addition, in the case of cutting the both ends 120 of the composite film 100, the width of the cutting is the width of the two ends 120 from the most protruding part of both sides toward the central part 110. The preferred width is The width is 30 mm or less, more preferably 10 mm or less, and more preferably 5 mm or less. Thus, while the side surfaces of both end portions 120 can be made smooth, the amount of both end portions 120 to be removed by cutting can be reduced, so the amount of the second thermoplastic resin used to form both end portions 120 can be reduced. Conducive to saving costs.

In addition, in this embodiment, the composite film 100 from which both ends 120 have been cut out in this way is wound up by a composite film winding roll (not shown), whereby the composite film 100 can be continuously obtained.

stretching process

The stretching step is a step of heating and stretching the composite film 100 obtained in the composite film forming step in the longitudinal direction and the width direction. Here, FIG. 2 is a diagram for explaining the stretching step. In the stretching process of this embodiment, the composite film 100 is sent out from the composite film winding roll, and as shown in FIG. The composite film 100 is heated and stretched by a synchronous biaxial stretching method in which the composite film 100 is stretched simultaneously in the horizontal direction and the width direction.

Specifically, in the stretching process, the composite film 100 is continuously sent out from the composite film winding roll, and the both ends 120 of the composite film 100 are held at constant intervals using a plurality of clamps, and the composite film is stretched by each clamp 310. The composite film 100 is transported to the stretching furnace 320 , and in the stretching furnace 320 , the composite film 100 is stretched in the longitudinal direction and the width direction by the respective clips 310 to be stretched. At this time, the composite film 100 is conveyed while being held by the clamps 310 and passes through the stretching furnace 320 . After the glass transition temperature of the second thermoplastic resin in both ends 120 is higher by about 10°C to 30°C, in the stretching belt in the stretching furnace 320, the composite film 100 is kept at the temperature by using a clip. 310 stretches the composite film 100 lengthwise and widthwise so that it expands lengthwise and widthwise. Then, the stretched film can be obtained by cooling and solidifying the stretched film in a cooling thermosetting belt. Then, the stretched film can be obtained continuously by opening the clamp 310 and winding it up with a roll.

In addition, in the present embodiment, the stretched film may be obtained by making the stretching step and the composite film forming step a continuous continuous line (process).

In the present embodiment, a pair of guide rails for moving the clips 310 is provided to allow the composite film 100 to pass through the stretching furnace 320 . A pair of guide rails are respectively arranged on the positions of the clamps 310 that hold the upper side of the two ends 120 of the composite film 100 shown in FIG. In the preheating zone in the furnace 320, a pair of guide rails are parallel to each other. In the stretching zone, the pair of guide rails are separated from each other along the width direction of the composite film 100. In the cooling heat curing zone, the pair of guide rails are parallel to each other. Alternatively, it is also possible to set the distance between a pair of guide rails in the cooling thermosetting belt in consideration of the shrinkage of the stretched film after being heated and stretched in the stretching belt when it is solidified in the cooling thermosetting belt. Based on the width when the stretched film is positioned on the output side of the stretching belt, they are close to each other by about several percent in the width direction. In the present embodiment, the composite film 100 can be conveyed and stretched by moving the grippers 310 holding both ends 120 of the composite film 100 along such guide rails.

In the present embodiment, the composite film 100 is stretched in a stretching belt in a stretching furnace 320 using a gripper 310 moving along such rails. That is, in the stretching belt in the stretching furnace 320, the grippers 310 that hold the both ends 120 of the composite film 100 are moved so as to be apart in the width direction along the guide rails, and at the same time, the grippers 310 are separated from each other. Controlling the expansion of the gap, the both ends 120 of the composite film 100 are stretched in the longitudinal direction and the width direction as shown by the arrows in FIG. 2 . Thus, the central portion 110 and both end portions 120 of the composite film 100 are heated and stretched in the longitudinal direction and the width direction respectively to a required stretching ratio. Then, the heated and stretched composite film 100 is cooled and solidified in the cooling thermosetting belt in the stretching furnace 320, and is wound up with a roll provided outside the stretching furnace 320, thereby continuously obtaining a stretched film 100. Stretch film.

In addition, in this embodiment, the thickness of the central portion 110 of the composite film 100 after heat stretching is preferably 15 μm to 50 μm, more preferably 20 μm to 40 μm. By controlling the thickness of the central portion 110 of the composite film 100 after heating and stretching within the above range, it is possible to prevent the composite film 100 from being broken during the heating and stretching, and to perform heating and stretching of the composite film 100 appropriately.

In addition, in the present embodiment, for the stretched film obtained by heat-stretching the composite film 100 , the portions of both ends 120 may be cut as necessary. Thereby, the stretched film can be made into the film which consists of the center part 110 only.

As described above, in this embodiment, by using the composite film forming process, the composite film 100 including the central portion 110 made of the first thermoplastic resin and the both end portions 120 made of the second thermoplastic resin is formed, and the formed composite film 100 is formed. After smoothing both side surfaces of both end portions 120 of the film 100, the central portion 110 and both end portions 120 of the composite film 100 are heated and stretched in a stretching process to obtain a stretched film. Thus, according to the present embodiment, it is possible to prevent the composite film 100 from being broken when the composite film 100 is heated and stretched, and it is possible to improve the productivity of the stretched film.

In addition, in a conventionally known method, for a film obtained by melt-extruding a thermoplastic resin with a molding die, in order to prevent the film from breaking when heating and stretching by a simultaneous biaxial stretching method, the film before heating and stretching The both end portions are formed thicker than the central portion. However, this method has the following problems: the shape of both sides of the film becomes uneven and rough due to uneven extrusion of the forming die, etc., and stress concentrates on the film when the film is stretched by the jig 310. The roughened parts on both sides of the film cause the film to break easily. At this time, as a method of smoothing both sides of the film, it is conceivable to adjust the extrusion rate of the molding die, adjust the positions of the touch roll 230 and the cooling roll 240, and the conveying speed. method, it is difficult to sufficiently smooth both sides of the film. In addition, in the method of increasing the thickness of both end portions of such a film, there is also a problem that the amount of thermoplastic resin required to obtain a stretched film increases, which is disadvantageous in terms of cost.

In view of this, the inventors of the present invention paid attention to the problem that, as a characteristic of a thermoplastic resin used for producing a stretched film, the elongation at break (expressed when stretched to The value of the elongation of the dimension when the film is broken relative to the dimension before stretching) is several hundred percent, which is relatively large. On the other hand, in the actual manufacturing process shown in FIGS. When a film made of this thermoplastic resin is heated and stretched, the film is broken at an elongation lower than the above-mentioned elongation at break. rough. In addition, the inventors of the present invention found a method based on the above findings: by smoothing the side surfaces of both ends 120 of the composite film 100 before heating and stretching, it is possible to prevent the composite film 100 from being damaged by heating and stretching. fracture.

In particular, according to the present embodiment, as a method of smoothing the both sides of the both ends 120 of the composite film 100, by adopting the method of cutting the ends 120 as described above, the composite film 100 is heated and stretched. When stretching, not only can the composite film 100 be prevented from being broken due to the roughness of the both sides of the two end portions 120, but also can prevent the occurrence of a portion where the thickness of the boundary portion between the central portion 110 and the two end portions 120 becomes thinner as follows. Cracked.

That is, the composite film 100 melt-extruded from the T-die 220 is pulled by the cooling roll 240 immediately after being melt-extruded, thereby causing a phenomenon called neck-in that elongates in the longitudinal direction and shrinks in the width direction. It is considered here that when the composite film 100 is stretched in the longitudinal direction by the cooling roll 240, the shrinkage of the thermoplastic resin in the width direction can be suppressed due to the presence of the adjacent thermoplastic resin in the central portion 110 of the composite film 100. , the force that causes the central portion 110 to shrink only in the thickness direction acts. That is, the central portion 110 is considered to be composed of the first thermoplastic resins juxtaposed in the width direction, and therefore, the shrinkage of the entire central portion 110 in the width direction can be suppressed by mutually stretching adjacent resins. On the other hand, in both end portions 120, although one end portion is adjacent to the central portion 110, but there is no resin adjacent to the central portion 110 at the other end portion, it is considered that there is no resin adjacent to the central portion 110 except in the thickness direction. A force that shrinks both end portions 120 acts, and a force that shrinks both end portions 120 in the width direction also acts. Therefore, when neck-in occurs, at the boundary between the central portion 110 and both end portions 120 where stress is applied in a different manner, the thermoplastic resin is stretched toward the both end portions 120 , causing the thickness of the boundary portion to change. Tendency to be thin. In this case, if the thickness of the both end portions 120 is too thick compared to the thickness of the boundary portion between the central portion 110 and the both end portions 120, stress will occur when the composite film 100 is heated and stretched in the stretching process. Concentrations are concentrated at the thin boundary portion, and cracks are likely to occur at the boundary portion.

In this regard, if the both ends 120 of the composite film 100 are cut, the thicker parts of the both ends 120 can be removed by cutting, so the thickness between the two ends 120 and the above-mentioned boundary can be reduced. When the composite film 100 is heated and stretched, it is possible to suppress the stress from concentrating on the boundary portion, and it is possible to effectively prevent cracks from occurring at the boundary portion.

In addition, conventionally, in order to prevent the composite film 100 from breaking when heating and stretching, a known method is to add rubber elastic particles to the both ends 120 of the composite film 100 to soften the two ends 120 (increasing the breaking elongation at room temperature). length) method. However, in this method, since the rubber elastic particles in both end portions 120 are easily deteriorated by heat, there is a problem as follows. That is, when the composite film 100 is melted and co-extruded from the T-die 220, rubber elastic particles degraded by heat are precipitated on the lip 222 of the T-die 220 to form deposits, which may cause damage to the film due to the deposits. There is a possibility that the composite film 100 will be indented, or deposits may be mixed into the product roll of the stretched film, thereby deteriorating the quality of the stretched film. Moreover, if such deposits of rubber elastic particles are formed, the deposits may enter between the composite film 100 and the clips 310 when the composite film 100 is heated and stretched by the clips 310 as shown in FIG. As a result, the composite film 100 may be easily broken.

On the other hand, according to this embodiment, it is not necessary to add such rubber elastic particles to the both ends 120 of the composite film 100, or the amount of rubber elastic particles added to the both ends 120 can be reduced, therefore, it is possible to suppress When the composite film 100 is melt-coextruded, rubber elastic particles are precipitated, so that the quality of the obtained stretched film can be excellent.

In addition, in this embodiment, as the first thermoplastic resin for forming the central portion 110, it is only necessary to select according to the application of the desired stretched film, for example, acrylic resin (PMMA), cyclic olefin copolymerized resin, etc., can be used. substance (COC), etc.

In addition, as the second thermoplastic resin, as long as it is a thermoplastic resin that can properly smooth the side surfaces after forming the both end portions 120 of the composite film 100, for example, it is preferable to use a thermoplastic resin having a higher ductility at the both end portions 120 than the central portion 110. Highly ductile thermoplastic resin. Specifically, as the second thermoplastic resin, it is preferable to use a thermoplastic material having a higher elongation at break at room temperature at both ends 120 than at room temperature at the center 110 of the composite film 100 before heating and stretching. resin. In addition, the elongation at break at normal temperature is a value indicating the elongation of the dimension when the center portion 110 and both end portions 120 are broken when stretched in a normal temperature environment of about 10°C to 30°C, relative to the dimension before stretching. . Thereby, the stress applied to the composite film 100 when cutting the both ends 120 of the composite film 100 can be relaxed, and it is possible to effectively prevent the composite film 100 from being cracked during cutting.

In particular, when the both ends 120 of the composite film 100 are cut, if the elongation at break of the central part 110 at room temperature is low at 10% or less, due to the stress applied to the composite film 100 during cutting, There is a possibility of cracking the central portion 110 . In this regard, as described above, as the second thermoplastic resin, by using a thermoplastic resin having a higher elongation at break at room temperature at both end portions 120 than at room temperature at the center portion 110, it is possible to ease the tension during cutting. The stress can effectively prevent the central portion 110 from cracking.

Furthermore, as the second thermoplastic resin, it is preferable to use a thermoplastic resin having a difference (|Tg ₁ −Tg ₂ |) between the glass transition temperature Tg ₁ of the first thermoplastic resin and the glass transition temperature Tg ₂ of the second thermoplastic resin of 10°C or less. resin. Thus, in the present embodiment, when heating and stretching the both ends 120 of the composite film 100 held by the jigs 310 in the stretching process, the both ends 120 held by the jigs 310 are heated by the stretching furnace 320 and then heated by the stretching furnace 320 . On the other hand, moderate softening can prevent the jig from falling off during heating stretching, breakage of the composite film 100 , and the like, thereby improving the productivity of the stretched film.

In addition, at this time, the difference between the glass transition temperature of the first thermoplastic resin and the glass transition temperature of the second thermoplastic resin (|Tg ₁ -Tg ₂ |) is preferably 10°C or less, more preferably 5°C or less, and still more preferably below 3°C.

In this embodiment, as the second thermoplastic resin, specifically, the following thermoplastic resins can be used from the above viewpoint. For example, when an acrylic resin is used as the first thermoplastic resin, one of polyethylene naphthalate (PEN), cycloolefin polymer (COP), and the like can be used alone as the second thermoplastic resin. , or a mixed resin obtained by mixing two or more of the above-mentioned materials can be used.

In addition, as the second thermoplastic resin, a resin obtained by adding a small amount of rubber elastic particles to the above-mentioned first thermoplastic resin may be used as long as the productivity of the stretched film is not hindered.

Alternatively, as the second thermoplastic resin, a thermoplastic resin (heat-resistant thermoplastic resin) having a glass transition temperature higher than that of the first thermoplastic resin and having a difference of more than 10° C. from the glass transition temperature of the first thermoplastic resin can be used. A mixed resin obtained by mixing a thermoplastic resin (low-temperature meltable thermoplastic resin) that has a lower glass transition temperature than the first thermoplastic resin. At this time, it is preferable to adjust the glass transition temperature of the obtained mixed resin by adjusting the mixing ratio between the heat-resistant thermoplastic resin and the low-temperature melting thermoplastic resin so that the glass transition temperature of the first thermoplastic resin The difference between the transition temperature and the glass transition temperature of the second thermoplastic resin (|Tg ₁ −Tg ₂ |) is within the above range.

For example, when using an acrylic resin with a glass transition temperature Tg1 _of about 120°C as the first thermoplastic resin, as the second thermoplastic resin, a polycarbonate resin having a higher glass transition temperature of about 150°C can be used. Polyethylene terephthalate (PET), which has a lower glass transition temperature of about 70°C, is mixed with ester (PC) to adjust the glass transition temperature to the same level as the glass transition temperature _Tg1 A mixed resin obtained at around 120°C.

In addition, when such a mixed resin is used as the second thermoplastic resin, polycarbonate (PC), cycloolefin polymer (COP), or the like can be used as the heat-resistant thermoplastic resin. In addition, polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), acrylonitrile-butadiene-styrene ( ABS), polyethylene (PE), acrylic resin having a lower glass transition temperature than the first thermoplastic resin, polyester (PES), polybutylene terephthalate (PBT), and the like. In the present embodiment, among these materials, polycarbonate (PC) is preferably used as the heat-resistant thermoplastic resin from the viewpoint of easy adjustment of the glass transition temperature of the mixed resin obtained, and polycarbonate (PC) is preferably used as the low-temperature melting resin. As the thermoplastic resin, polyethylene terephthalate (PET) is preferably used.

In addition, in the above example, the following example is shown as a method of producing the composite film 100 using such a first thermoplastic resin and a second thermoplastic resin: as shown in FIG. However, in this embodiment, as shown in FIG. 3 , a method of drawing the composite film 100 using only the cooling roll 240 without using the touch roll 230 may also be used. In this way, the distance between the T-die 220 and the cooling roll 240 can be shortened, and the necking ( Due to the phenomenon that the composite film 100 is stretched in the longitudinal direction while being pulled by the cooling roll 240 and the width is narrowed), the resulting composite film 100 can be suppressed from shrinking due to neck-in, thereby suppressing uneven thickness.

In addition, in the above-mentioned example, an example was shown in which the both ends 120 of the composite film 100 before heating and stretching were cut to smooth the side surfaces of the both ends 120, but in this embodiment, as the two The method of smoothing the side surfaces of the end portions 120 is not particularly limited, and methods such as grinding the ends of the both end portions 120 and hot extrusion molding the ends of the end portions 120 may be used.

In addition, in the above-mentioned example, as a method of heating and stretching the composite film 100, as shown in FIG. As an example of the stretching method, however, in the present embodiment, a method of uniaxially stretching the composite film 100 only in the longitudinal direction may also be used.

At this time, heating and stretching of the composite film 100 in the longitudinal direction can be performed in the same manner as the simultaneous biaxial stretching method shown in FIG. 2 . That is, a method of transporting the composite film 100 into the stretching furnace 320 while holding both ends 120 of the composite film 100 with the jigs 310, and then, in the stretching furnace 320, the person holding the composite film 100 can be used. Each clip 310 of both end parts 120 is moved in the width direction, but heat-stretching is performed only in the longitudinal direction by increasing the distance between the clips 310 .

In this embodiment, regardless of whether simultaneous biaxial stretching is performed in the longitudinal direction and the width direction or in the case of uniaxial stretching only in the longitudinal direction, by using the jig 310 as shown in FIG. Stretching while holding the both ends 120 of the composite film 100 can improve the productivity of the stretched film and improve the quality of the stretched film obtained compared with the conventional sequential biaxial stretching method.

In addition, the conventional sequential biaxial stretching method is a method of heating and stretching the composite film 100 produced by the method shown in FIG. 1 first in the longitudinal direction and then heating and stretching in the width direction. In the sequential biaxial stretching method, after the composite film 100 is heated and stretched in the longitudinal direction by conveying the composite film 100 with a plurality of rollers, as shown in FIG. 120 while heating and stretching the composite film 100 in the width direction.

Here, in the sequential biaxial stretching method, specifically, the composite film 100 is stretched in the longitudinal direction as follows. That is, the sequential biaxial stretching method is adopted, and the composite film 100 is preheated to about the glass transition temperature of both ends 120 while conveying the composite film 100 by a plurality of preheated preheating rolls, and then heated by infrared rays. The preheated composite film 100 is further heated to a temperature about 10° C. to 30° C. higher than the glass transition temperature of both ends 120 by using a device or the like, and the composite film 100 is continuously conveyed by cooling rolls. At this time, by making the conveying speed of the cooling roller faster than the conveying speed of the preheating roller, tension is generated between the preheating roller and the cooling roller, and the composite film 100 is stretched in the longitudinal direction to the required tension by using the tension. Magnification.

Here, in the sequential biaxial stretching method, when the composite film 100 is stretched in the longitudinal direction, since the surface of the composite film 100 is in contact with the preheating roll and the cooling roll, the surface of the composite film 100 may be rubbed. The appearance quality of the obtained stretched film deteriorates due to scratches. In addition, in the sequential biaxial stretching method, when the composite film 100 is heated and stretched in the longitudinal direction, since the positions of the two ends 120 of the composite film 100 in the width direction are not fixed, the composite film 100 may be damaged due to Heat shrinks in the width direction, thereby reducing the productivity of the stretched film.

In contrast, in this embodiment, by using the simultaneous biaxial stretching method or the method of uniaxial stretching only in the longitudinal direction (that is, as shown in FIG. The two ends 120 of 100 stretch the composite film 100 along the longitudinal direction) to carry out the stretching of the composite film 100 along the longitudinal direction, which can avoid the contact between the composite film 100 and the roller, so the heating and stretching can be reduced. After the surface of the composite film 100 is scratched. Thus, for the stretched film obtained by cutting the both ends 120 of the heated and stretched composite film 100, the appearance quality can be improved, and in particular, it can be preferably applied to optical films and the like that require strict appearance quality. . And, according to this embodiment, since the both ends 120 of the composite film 100 are held by the clips 310 when the composite film 100 is stretched in the longitudinal direction, it is possible to prevent the composite film 100 from shrinking in the width direction due to heat, thereby improving the tensile strength. stretch film productivity.

In addition, in the above example, the example in which the composite film 100 is formed of two resins, the first thermoplastic resin and the second thermoplastic resin, is shown. However, in this embodiment, the composite film 100 may be made of only the first thermoplastic resin. constitute. That is, both the central portion 110 and both end portions 120 of the composite film 100 may be formed of the first thermoplastic resin, and the composite film 100 may be a film composed of only the first thermoplastic resin.

At this time, the first thermoplastic resin is a resin determined according to the required stretched film, and when the film is formed by the T-die 220 and then both ends are cut, it is the same as the above-mentioned second thermoplastic resin. Compared with the case of the end portion 120, the smoothness of the side surface after cutting may be poor, but when cutting such a film made of only the first thermoplastic resin, the side surface of the film can be smoothed by adjusting the cutting conditions. It is sufficient to the extent that local stress concentration does not occur during heating and stretching.

Example

Hereinafter, although an Example is given and this invention is demonstrated more concretely, this invention is not limited to these Examples.

Example 1

As the first thermoplastic resin for forming the central portion 110 of the composite film 100, an acrylic resin (glass transition temperature Tg ₁ : 123° C., elongation at break at room temperature: 5%) was prepared as the first thermoplastic resin for forming the composite film 100. As the second thermoplastic resin at both ends 120 of 100, an acrylic resin (glass transition temperature Tg ₂ : 125° C., elongation at break at room temperature: 18%) added with a small amount of rubber elastic particles was prepared.

Here, for the first thermoplastic resin and the second thermoplastic resin, the glass transition temperatures of both were measured by differential scanning calorimetry (DSC), and measured by a tensile tester (manufactured by ORIENTEC CORPORATION, model: RTC-1210A) The elongation at break at room temperature for both. The same applies to the following Examples 2 to 4 and Comparative Examples 1 and 2.

Next, the prepared first thermoplastic resin and second thermoplastic resin were respectively supplied to the supply head 210 using a twin-screw extruder, and the composite film 100 was produced under the following conditions by the method shown in FIG. 1 . Here, the overall width of the produced composite film 100 is about 315 mm, wherein the regions with a width of about 50 mm from both ends are the two ends 120 , and the remaining central regions are the center 110 . In addition, the thickness of the central part 110 of the produced composite film 100 is about 150 μm to 170 μm, and the maximum thickness of both end parts 120 is about 400 μm. In addition, in this embodiment, the acrylic resin added with rubber elastic particles was used as the second thermoplastic resin, but since the amount of rubber elastic particles added is small, it is possible to suppress the occurrence of the rubber when the composite film 100 is melt-coextruded. The precipitation of elastic particles.

T-die 220 outlet width: 380mm

Air gap length: 60mm

Traction speed of chill roll 240: 6mpm

Supply amount of the first thermoplastic resin supplied to the supply head 210: 15kg/hr

Supply amount of the second thermoplastic resin supplied to the supply head 210: 5kg/hr

In addition, the above-mentioned air gap length represents the distance from the outlet of the thermoplastic resin of the lip 222 to the position pressurized by the cooling roll 240 and the touch roll 230 (ie, the position where the cooling roll 240 and the thermoplastic resin contact).

Next, after conveying the obtained composite film 100 by the cooling roll 240, the both end parts 120 are cut|disconnected continuously by a doctor blade (laser blade). In addition, cutting was performed by cutting out the area|region of 10 mm width from both side surfaces of the both ends part 120, respectively.

Next, for the composite film 100 with both ends 120 cut out, the both ends 120 are held by the clamps 310, and as shown in FIG. stretch.

Input side speed before heating and stretching: 1mpm

Output side speed after heating and stretching: 2mpm

Stretch ratio: 100% in the length direction x 100% in the width direction (twice in the length direction x twice in the width direction)

Gripping position of the jig 310: 15 mm from the end of the composite film 100

Preheating temperature, distance: 140°C, 350mm

Stretch belt temperature, distance: 140°C, 500mm

Cooling heat curing temperature, distance: 90°C, 700mm

In addition, in the present example, when the composite film 100 is heated and stretched continuously within a length range in which the productivity of the stretched film can be confirmed, the composite film 100 does not break, and thus the composite film 100 can be continuously produced. Excellent quality stretch film.

Example 2

As shown in FIG. 3 , as a method of producing the composite film 100, a method of pulling the first thermoplastic resin and the second thermoplastic resin melted and co-extruded from the T-die 220 by using only the cooling roll 240 without using the touch roll 230 is adopted. , so that the distance between the T-die 220 and the cooling roll 240 is shortened so that the air gap length (the distance from the outlet of the thermoplastic resin of the die lip 222 to the position where the cooling roll 240 contacts the thermoplastic resin) is 25 mm, in addition Except that, in the same manner as in Example 1, a stretched film was obtained.

In addition, in Example 2, the thickness of the central part 110 of the composite film 100 before cutting is about 140 μm to 180 μm, and the maximum thickness of the both end parts 120 is about 170 μm. The distance between the cooling rolls 240 suppresses the neck-in compared to the above-mentioned Example 1, and the both ends 120 are thinned, so that the composite film 100 as a whole becomes flat.

In addition, in Example 2, as in Example 1, the precipitation of rubber elastic particles when the composite film 100 is melted and coextruded can be suppressed, and the composite film 100 does not break during heating and stretching of the composite film 100. , can continuously produce stretched film with excellent quality.

Example 3

As the second thermoplastic resin for forming both ends 120 of the composite film 100, 25% by weight of polyethylene terephthalate (PET) was mixed with 75% by weight of polycarbonate (PC). A stretched film was obtained in the same manner as in Example 1 except for the obtained mixed resin (glass transition temperature Tg ₂ : 125° C., elongation at break at room temperature: 20%).

In addition, in Example 3, as in Example 1, the composite film 100 was not broken during heating and stretching of the composite film 100 , and a stretched film with excellent quality could be continuously produced.

Example 4

As the second thermoplastic resin for forming both ends 120 of the composite film 100, the same acrylic resin as the first thermoplastic resin was used (glass transition temperature Tg ₁ : 123°C, elongation at break at room temperature: 5%) ), thereby forming a single-layer film composed of only the above-mentioned acrylic resin as the composite film 100, except that, a stretched film was obtained in the same manner as in Example 1.

In addition, in Example 4, the thickness of the part corresponding to the central part 110 of the single-layer film before cutting is about 140 μm to 175 μm, and the maximum thickness of the part corresponding to both end parts 120 is about 310 μm, which is similar to the above-mentioned embodiment. In the same manner as in Example 1, both end portions 120 are thicker than the center portion 110 .

In addition, in Example 4, the elongation at break of the acrylic resin constituting the single-layer film at room temperature is as low as 5%, and the ductility is low. Therefore, when the single-layer film is cut, the side surface of the single-layer film and The above-mentioned Examples 1 to 3 were slightly rougher, and the single-layer film was broken only once when the single-layer film was continuously heated and stretched. Therefore, in Example 4, the occurrence frequency of breakage of the single-layer film during heating stretching was significantly low, and it was within a range that did not hinder the productivity of the stretched film. As a result, stretched films with excellent quality could be continuously produced. Stretch film.

Comparative example 1

A stretched film was obtained in the same manner as in Example 1 except that the both ends 120 were not cut after the composite film 100 was produced.

In addition, in Comparative Example 1, since the two ends 120 were not cut after the composite film 100 was produced, the sides of the two ends 120 were in a rough state. When the composite film 100 was heated and stretched, the composite film 100 Breakage occurs frequently, and the productivity of the stretched film decreases.

Comparative example 2

A stretched film was obtained in the same manner as in Example 2 except that the both ends 120 were not cut after the composite film 100 was produced.

In addition, in Comparative Example 2, since the two ends 120 were not cut after the composite film 100 was produced, the sides of the two ends 120 were in a rough state. When the composite film 100 was heated and stretched, the composite film 100 Breakage occurs frequently, and the productivity of the stretched film decreases.

As described above, for Examples 1 to 4 in which the side surfaces of the composite film 100 or the single-layer film before heating and stretching were smoothed, when the composite film 100 was heated and stretched, the composite film 100 could be suppressed from breaking, Therefore, a stretched film having excellent quality can be obtained, and the productivity of the stretched film can also be improved.

On the other hand, as described above, in Comparative Examples 1 and 2 in which the side surfaces of the composite film 100 before heating and stretching were not smoothed, when the composite film 100 was heated and stretched, the composite film 100 was frequently broken. , The productivity of the stretched film is poor.

Explanation of reference signs

100…Composite film

110…Central part

120...both ends

210…feed head

220…T type die

230…contact roller

240...cooling roll

250…cutter

310...Clamp

320…drawing furnace

Claims (9)

1. A manufacturing method of stretched film, is characterized in that, comprises: A pre-stretching film forming step in which the first thermoplastic resin and a second thermoplastic resin different from the first thermoplastic resin are melted and co-extruded from a self-forming die in the pre-stretching film forming step. 1. The thermoplastic resin and the second thermoplastic resin are then cooled to solidify the first thermoplastic resin and the second thermoplastic resin to form a central portion made of the first thermoplastic resin and formed along the width direction. The pre-stretched film at both ends of the central portion and at both ends of the second thermoplastic resin; A smoothing step in which, with respect to the film before stretching, a portion of the both ends is removed from both side surfaces of the both ends so that the thickness of the film before stretching is defined. Side smoothing; and a stretching step in which the smoothed both sides of the pre-stretched film is held at least along the Heat stretching in the longitudinal direction to form a stretched film. 2. The manufacturing method of the stretched film according to claim 1, characterized in that, Part of the both end portions are removed by removing a range of 30 mm or less in width from the both sides. 3. The manufacturing method of the stretched film according to claim 1, characterized in that, A part of the both ends are removed by cutting. 4. The manufacturing method of the stretched film according to claim 1, characterized in that, In the stretching step, the stretched film is stretched not only in the longitudinal direction of the stretched film but also in the width direction of the stretched film. The pre-stretching film is heated and stretched. 5. The manufacturing method of the stretched film according to claim 1, characterized in that, In the stretching step, the pre-stretched film is heated and stretched, so that the thickness of the stretched film after heating and stretching is in the range of 15 μm to 50 μm. 6. The manufacturing method of the stretched film according to claim 1, characterized in that, As the first thermoplastic resin and the second thermoplastic resin, when the film before stretching is formed by melt coextrusion, the thermoplastic resin composed of the second thermoplastic resin is used. The elongation at break at normal temperature at both end portions is greater than the elongation at break at normal temperature at the center portion made of the first thermoplastic resin. 7. The manufacturing method of the stretched film according to claim 1, characterized in that, An acrylic resin is used as the first thermoplastic resin. 8. The manufacturing method of the stretched film according to claim 7, characterized in that, As the second thermoplastic resin, polycarbonate is mixed with a thermoplastic resin having a glass transition temperature lower than that of the acrylic resin. 9. The manufacturing method of the stretched film according to claim 1, characterized in that, As the first thermoplastic resin and the second thermoplastic resin, a thermoplastic resin having a glass transition temperature difference of 10° C. or less is used.